How many satellites are needed for a 3D position fix?

For a 3D position fix in Global Navigation Satellite System (GNSS) technology, a minimum of four satellites is required. This is essential for determining an exact position in three dimensions: latitude, longitude, and altitude.

When signals are received from three satellites, the system can calculate a 2D fix (latitude and longitude) based on the intersection of their signals. However, to accurately establish the altitude (which gives you the third dimension), a fourth satellite is necessary. The reason for this is that GNSS systems operate based on trilateration, and having an additional satellite allows the system to resolve the position in space while also accounting for variations in signal travel times caused by factors such as atmospheric conditions and clock offsets in the satellite signals.

Thus, utilizing four satellites enables the receiver to solve for both the three-dimensional coordinates and to synchronize the time effectively, which is crucial for accurate positioning.